1. Field of the Invention
This invention relates to an improved system for controlling thrust output of a gas turbine engine and, more particularly, to such a system which automatically adjusts the thrust output to compensate for changes in the engine due to aging.
2. Description of the Prior Art
One of the main functions of a gas turbine engine control system is to provide for the generation of whatever specific level of thrust is required or demanded by throttle position set by the pilot or engine operator. Due to quality variations, control tolerances and various other factors, no two engines are exactly alike in their operational characteristics. In addition, the operational characteristics of each engine tend to change as the engine ages, and some components deteriorate. Therefore, engine control systems must be designed to function with engines whose operational characteristics vary widely.
In order that such an engine control system is able to function to provide the guarantee on rated thrust level on all engines, it must be designed to control a "minimum" engine; that is, an engine which produces only the minimum rated thrust due to the above described variations. An engine control system which is designed to adequately operate with a "minimum" engine ends up producing excessive thrust levels with "average" or "above average" engines. These excessive thrust levels cause the engines to operate at higher temperatures than would otherwise be necessary to provide rated or desired thrust, thereby potentially decreasing the operating life of the engine. This problem is even further compounded as the engines age, and the thrust output tends to increase even more.
It is, therefore, an object of the present invention to provide an improved gas turbine engine thrust control system which adjusts the thrust output of the engine as it ages in order to maintain a substantially fixed relationship between the thrust output and the demanded thrust level.
It is another object of the present invention to provide such a thrust control system which automatically trims each individual engine to the lowest possible operating engine thrust level consistent with the rated engine thrust level.
It is a further object of the present invention to provide such a thrust control system which allows for lower design temperature margins, thereby increasing engine life.
It is yet another object of the present invention to provide such a thrust control system with built-in redundancy for increased operational safety.